In the conventional manufacturing of silicon single crystal by a CZ method, a small piece of a single crystal silicon is used as a seed crystal, and this is brought into contact with a raw material melt (a silicon melt) and slowly pulled with rotation to grow a silicon single crystal rod (ingot).
In this operation, after the seed crystal is brought into contact with the raw material melt (seeding), the so-called necking is generally performed (Dash Necking method), which forms a tapered necking part to neck the seed crystal and a subsequent neck portion with the diameter being once decreased to about 3 mm, in order to eliminate dislocations produced by propagation of slip dislocations (also referred to as slip simply) generated in the seed crystal at a high density by thermal shock.
After the seed crystal is brought into contact with a raw material melt and is subjected to necking as described above, the single crystal is enlarged to have a desired diameter to form an enlarging diameter portion (also referred to as a cone portion) (a cone forming step). Then, the straight body portion is grown (a straight body forming step), and subsequently, a tail portion is grown while gradually decreasing the diameter of the straight body portion (a tail forming step). The grown silicon single crystal is separated from the melt, and the silicon single crystal is gradually cooled (an after-heating step). By such procedures, dislocation-free silicon single crystals have been grown.
Previously, it has been proposed various technologies to pull such a dislocation-free silicon single crystal.
For example, Patent Document 1 discloses a preferable interstitial oxygen concentration introduced during necking in order to suppress an increase of dislocations in seeding.
In addition, the diameter of a silicon wafer for a semiconductor device has been increased recently, and a wafer with a diameter of 300 mm or more, further with a diameter of 450 mm or more has been highly demanded. Under this circumstance, it has been increasing to manufacture a silicon single crystal for manufacturing a silicon wafer with a diameter of 450 mm.